Bleach. If your dog is being reinfected monthly, you need to treat your dog or treating the yard is useless. Hooks are really a bear to treat. I tried Panacur twice from our Vet and one round of Drontal, with no avail from the little bastiages.
You really need to worm the heck out of a dog to get rid of hookworms. Drontal Plus several times in a row should get rid of them. I treated Danger with Drontal Plus for three days in a row, waited a week, repeated three days again with the Drontal Plus, waited two weeks and treated again for three days with Drontal Plus. That finally got rid of them.
I got the Drontal Plus from an AU site, much cheaper than the Vet and no 'script needed.